[pulseaudio-discuss] Bluetooth A2DP aptX codec quality

ValdikSS iam at valdikss.org.ru
Fri Sep 14 12:39:40 UTC 2018

On 12/09/2018 19:03, Luiz Augusto von Dentz wrote:
>> 2) Should we rather look at increasing quality of SBC codec in
>> pulseaudio? And if yes, how should be quality of SBC configured? Via
>> profiles? Or to invent some new protocol options? Can we increase
>> default SBC bitpool allocation?
> I recall setting it to 64 before, but perhaps we are using 53 given
> that most headset set that as maximum influenced by the spec suggested
> values, I wouldn't go above 512kbit/s since then leave very little
> room for any other traffic.

I propose to use 76 bitpool as a default maximum (454.8 kbps for Joint Stereo, 44.1 kHz, 8 subbands, 16 blocks). This bitpool is optimal for both EDR 2 mbit/s and EDR 3 mbit/s modes, since it packs audio frames with least wasted bytes possible.
EDR 2 mbit/s: up to 4 audio frames, 11.7 ms, 2 wasted bytes
EDR 3 mbit/s: up to 6 audio frames, 17.5 ms, 14 wasted bytes.

Note that Pulseaudio/bluez (not sure which) does not manage L2CAP MTU correctly. For EDR 2 mbit/s, MTU should be set to 679 (ignoring higher values upon negotiation), and EDR 3 mbit/s should use 1021 (right now something like 800 is used).

>> 3) If aptX is decided as useless, what about aptX HD codec? aptX HD
>> codec is supported by less products (currently I do not own any), but
>> this one may provide better quality as SBC according to that research.
> That is probably useful as something that provides a quality
> improvement compared to SBC.
>> PS: That aptX research is the first and the only one about which I know.
>> All other information about quality or other details which I found on
>> internet are just marking informations.
> I had some suspicion before given that no manufacturer provided any
> evidence aptX would beat SBC at the same bitrate, it is probably
> better just because we are stuck at 53 bitpool with SBC while aptX can
> probably have much higher bitrate. Anyway thanks to the researcher for
> putting the time to evaluate the codecs we now have a good reference
> for the quality each codec provides.
>> --
>> Pali Rohár
>> pali.rohar at gmail.com
>> _______________________________________________
>> pulseaudio-discuss mailing list
>> pulseaudio-discuss at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss

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